As I read it a newly discovered macrophage appears to prevent older adults from burning belly fat. MAOA seems to restore normal fat metabolism; at least in the older mice.

Quote:

The researchers found that when they lowered a specific receptor that controls inflammation, the NLRP3 inflammasome, in aged macrophages, the catecholamines could act to induce fat breakdown, similar to that of young mice.

"The key finding is that the immune cells talk to the nervous system to control metabolism," said Dixit.

In further experiments, the researchers blocked an enzyme that is increased in aged macrophages, restoring normal fat metabolism in older mice. Dixit noted that this enzyme, monoamine oxidase-A or MAOA, is inhibited by existing drugs in the treatment of depression. "Theoretically one could repurpose these MAOA inhibitor drugs to improve metabolism in aged individuals," he said. But he also cautioned that more research is needed to specifically target these drugs to belly fat and to test the safety of this approach.